Earlier quoted context omitted.
I’m unaware of any Core Banking Systems (CBS) that runs on a cloud provider with the exception being Finastra (Azure). Other parts of retail banking stacks? Sure. Not their cores.
The major cloud providers all aim for 99.999% uptime. Keep in mind that 99.99% uptime means ~4 minutes of downtime a month. I think there are other reasons that banks may not want or have the ability to run their core services on the cloud.
It’s atypical motivation but one of the few verticals I know of where the cloud is largely out of the equation.